From what I understand, Pound is a load-balancing tool whilst Nginx is in fact a fully featured web server in its own right.
Nginx therefore addresses a much larger problem set than Pound whilst still proving extremely efficient and 'easy-to-configure' reverse-proxy and load sharing capabilities.
Nginx seems to be particularly well suited to acting as a front-end dispatcher, serving static resources itself and handing off other requests to other webservers behind the scenes. So if you have a whole load of different technologies in action (e.g. some OpenACS services, perhaps a PHP service and some other CGI based content), Nginx can serve the static resources immediately, and can reverse-proxy the other requests to the various backend webservers. This can be done whilst preserving the integrity of your access logs.
Furthermore, Nginx can be configured to handle the ssl element of https transactions so that you can have a single certificate providing encrypted access to several backend servers without having to configure an https listener on each one.
Just a few of my first thoughts.
Hope it helps
R.
